1. Field of the Invention
The present invention relates to a method of mounting and tensioning a freely tensioned tension member, particularly a stay cable for a cable-stayed bridge, and a device for carrying out the method.
2. Description of the Related Art
Tension members are frequently used in civil engineering for anchoring structural components; such tension members are, for example, stay cables for cable-stayed bridges or the like and are frequently composed of a bundle of individual elements, such as steel wires or steel strands. Along the free length of the tension member, the individual elements are arranged together in a tubular sheathing; for anchoring the tension members they are longitudinally movably guided through the respective structural components and are anchored at the side of the respective structural component located opposite the entry point of the individual element. The anchoring systems include an anchoring disk with bores through which the individual elements are passed and relative to which they are anchored, for example, by means of multipart annular wedges. Along the free length of the tension member, the tubular sheathing may be a plastic pipe, for example, of polyethylene, or a steel pipe. In the anchoring range, the sheathing tube usually is an anchoring pipe of steel. If the individual elements themselves are protected against corrosion, the hollow space between the individual elements and the tubular sheathing may remain unfilled or, after tensioning of the individual elements, a corrosion protection substance, for example, grease, or a hardening material, for example, cement mortar, may be pressed into the hollow space.
Particularly in stay cables of cable-stayed bridges, a problem is posed by the fact that the heavy cables must be mounted in the required inclined position between the anchoring systems for the cables in the girder supporting the roadway and at the top of the tower, frequently at great heights. There are several methods for assembling the stay cables on the work plane, for example, on the floor plate of the already finished bridge portion and for raising the stay cables by means of appropriate lifting apparatus into the required inclined position, or for producing an inclined template on scaffolding for the assembly of the stay cables and threading the individual elements placed on the template into the sheathing pipe. Finally, it is also known in the art to join the individual elements freely tensioned to form a bundle and to mount the tubular sheathing only subsequently. In each case, the individual elements must be threaded into the lower and upper anchoring systems before they can be tensioned.
In order to avoid the weight resulting from filling out the hollow space between the individual elements and the tubular sheathing with a corrosion protection material, the individual elements used for such tension members frequently are strands of steel wire which are covered with a layer of grease as corrosion protection and are surrounded by a casing of polyethylene. While such strands encased with polyethylene can be used as tension members in the same manner as bare strands, it is necessary to remove this polyethylene casing in the area of the anchoring systems, so that the wedges used for anchoring can act directly on the strands. For reasons of corrosion protection, it is especially important in the case of tension members in which the hollow space in the anchoring area remains unfilled to remove the polyethylene casing from the strand in such a way that in the final state, i.e., when the strand is tensioned, the remaining polyethylene casing ends as close as possible to the respective anchoring wedges independently of tolerances in cutting to length and of construction inaccuracies.